On Fri, 2009-10-09 at 12:43 +0200, Peter Zijlstra wrote:> On Fri, 2009-10-09 at 17:19 +0800, Zhang, Yanmin wrote:> > Comparing with 2.6.31's results, hackbench has some regression on a couple of> > machines woth kernel 2.6.32-rc1.> > I run it with commandline:> > ../hackbench 100 process 2000> > > > 1) On 4*4 core tigerton: 70%;> > 2) On 2*4 core stoakley: 7%.> > > > I located below 2 patches.> > commit 29cd8bae396583a2ee9a3340db8c5102acf9f6fd> > Author: Peter Zijlstra <a.p.zijlstra@chello.nl>> > Date: Thu Sep 17 09:01:14 2009 +0200> > > > sched: Fix SD_POWERSAVING_BALANCE|SD_PREFER_LOCAL vs SD_WAKE_AFFINE> > > > and > > Should I guess be solved by turning SD_PREFER_LOCAL off, right?> > > commit de69a80be32445b0a71e8e3b757e584d7beb90f7> > Author: Peter Zijlstra <a.p.zijlstra@chello.nl>> > Date: Thu Sep 17 09:01:20 2009 +0200> > > > sched: Stop buddies from hogging the system> > > > > > 1) On 4*4 core tigerton: if I revert patch 29cd8b, the regression becomes> > less than 55%; If I revert the 2 patches, all regression disappears.> > 2) On 2*4 core stakley: If I revert the 2 patches, comparing with 2.6.31,> > I get about 8% improvement instead of regression.> > > > Sorry for reporting the regression later as there is a long national holiday.> > No problem. There should still be plenty time to poke at them before .32> hits the street.> > I really liked de69a80b, and it affecting hackbench shows I wasn't> crazy ;-)> > So hackbench is a multi-cast, with one sender spraying multiple> receivers, who in their turn don't spray back, right?Right. volanoMark has about 9% regression on stoakley and 50% regressionon tigerton. If I revert the original patches, volanoMark regression on stoakleydisappears, but still has about 45% on tigerton.

> > This would be exactly the scenario that patch 'cures'. Previously we> would not clear the last buddy after running the next, allowing the> sender to get back to work sooner than it otherwise ought to have been.> > Now, since those receivers don't poke back, they don't enforce the buddy> relation...> > > /me ponders a bit> > Does this make it any better?I apply this patch and another one you sent on tbench email thread.On stoakley, hackbench is recovered. If reverting the original 2 patches,we get 8% improvement.On tigerton, with your 2 patches, there is still about 45% regression.

As for volanoMark, with your 2 patches, regression disappears on staokleyand it becomes about 35% on tigerton.

aim7 has about 6% regression on stoakley and tigerton. I didn't locate theroot cause yet.

The good news is only tbench has about 6% regression on Nehalem machines.Other regressions such like hackbench/aim7/volanoMark is not clear/big onNehalem. But reverting the original 2 patches don't fix the tbench regressionon Nehalem machines.